The present invention relates to an etching method. More specifically, the present invention relates to a dry etching method in which a deep trench or hole (hereinafter collectively referred to as "deep trench") can be effectively formed at a high precision on a semiconductor substrate.
Dry etching of a single crystal of silicon have been reported in many literature references, for example, Proc. Dry Process Symposium, page 121 (1984), and many methods have been proposed. Moreover, a method for forming a deep trench on a single crystal silicon substrate by dry etching is disclosed, for example, in Kure et al., Preprints of Lectures, Japanese Society of Applied Physics, 44th Autumn Meeting (1983), page 263.
In the conventional Si etching method, a chloride gas such as CCl.sub.4 or SiCl.sub.4 or a bromide gas such as CBrF.sub.3 is used as the reaction gas, but the etching speed is as low as about 1000 .ANG./min and 30 minutes are necessary for forming, for example, a trench having a width of 1.0 .mu.m and a depth of 3 .mu.m. Furthermore, since the time required for etching is long, wearing of a mask is violent, and because of retreat of the edge portion of the mask, the width of the trench is changed by about 0.1 .mu.m from the original size of the mask and it is difficult to form a trench at a high precision. Furthermore, in connection with the mask, a mask pattern having a thickness sufficient to resist etching to be conducted for such a long time as 30 minutes should be formed, and the precision of the size of the mask is low and a material having a sufficient etching resistance should be used as the mask material. Therefore, it is difficult to use a photoresist film as the mask.